The invention relates to a weighing sensor with a base that is fixed to the housing, a load sensor connected to the base in a displaceable manner using two arms, a lever system that has at least one lever and that transmits the load acting on the load sensor to a transducer, and a built-in calibration weight that can be lowered onto a support region to check and/or calibrate the sensitivity of the weighing sensor. The support region is parallel-guided using two additional arms and is connected to a lever of the lever system using a coupling element.
Weighing sensors of this type are known, for instance, from German Patent Specification DE 196 05 087 C2. They are preferably used in high-resolution scales for maximum loads of between 100 g and 100 kg. The lever system reduces the load acting on the load sensor to a smaller load that is capable of being processed by the transducer. The transducer that is often used is the coil/magnet combination of an electromagnetic force compensation. Other transducers, however, may be used instead, e.g., vibrating strings or strain gauges. The built-in calibration weight acts on a lever of the lever system and makes it possible to simulate a relatively large load on the load sensor with a relatively small calibration load. The two additional arms of the parallel guidance for the support region of the calibration weight connect the support region with the base fixed to the housing and thereby ensure a certain independence of the location where the calibration weight is supported. However, they cause substantial space problems in the space between the load sensor, the base fixed to the housing and the two arms. As a result, they significantly restrict the design options for the lever system and the additional parallel guidance, and also tend to increase the overall height of the weighing sensor.
To obviate these disadvantages, it has already been proposed (DE 100 07 267) to accommodate the calibration weight not in the space defined by the load sensor, the base fixed to the housing and the arms, but instead on the other side of the load sensor, by extending one lever arm of the lever system through the load sensor, and to lower the calibration weight directly onto this lever arm. However, lowering the calibration lever onto a lever arm of a transmission lever causes the action of the calibration weight to strongly depend on the location where the weight is supported. As a result, the lifting device or weight support must be very precise and consequently becomes costly.
Similarly, German Laid Open Document DE 199 53 987 A1 proposes to extend a transmission lever using two metal plates that are laterally attached by screws, and to provide each of these extension plates with a notch for receiving a calibration weight. The calibration weight is therefore again lowered onto a transmission lever, so that the strong location dependence described above is present in this variant as well.